Arthroplasty surgery is currently the most reliable and successful orthopedic treatment for osseous joint failure due to arthritis pain or severe physical joint damage. In the USA, around 200,000 patients receive hip replacement surgeries each year. Similar surgical procedures are performed also on other joints, including shoulders, elbows and knees. The articulating surfaces of the artificial joint prosthesis are commonly fabricated from three combinations of bearing materials: (i) ultra-high molecular weight polyethylene articulating against a metal (or ceramic) femoral head replacement (i.e. a metal on plastic (MOP) couple), (ii) a metal-on-metal (MOM) couple, or (iii) a ceramic-on-ceramic (COC) couple. MOM and COC articulations function with minimal wear and acceptable frictional resistance because of the presence of a thin layer of joint fluid which is held within the narrow space between the two highly polished counterfaces. This fluid layer keeps the surfaces apart and prevents direct contact between the metal-metal or ceramic-ceramic surfaces.
However, under some circumstances, the two counterfaces may come into contact due to loss of fluid over a focal area, or to increased roughening of the surface(s). When this occurs the lubrication of the bearing is said to have failed and wearing of the metal or ceramic surfaces will occur. A second form of unintended contact between the counterfaces occurs when the articulating components are rotated beyond their physical limits, leading to “impingement” or physical contact between the non-articulating surface of one component and the surface (articulating or non-articulating) of the other component. One example is a collision between the neck of the femoral component, directly below the modular head and the rim of the acetabular cup. This form of contact occurs when the patient places the femur in a position which exceeds the articulating range of motion (ROM) of the artificial joint. A third form of unintended contact leading to adverse wear of the artificial joint occurs when the head of the prosthesis is displaced from the center of the mating acetabular counterface. This can occur during joint motion and is often seen to cause the femoral head to “ride up” the lateral edge of the acetabular bearing, with loss of contact between the articulating surfaces over all but a small area. This form of motion is termed “micro-separation” and leads to high contact stresses and accelerated bearing wear.
The microscopic particles generated by the wear of artificial joint can lead to series inflammatory reactions, chronic pain, and permanent disability. In advanced cases, where this disease process has been left undetected, devastating loss of nerve and muscle tissue may occur, in addition to sensitization of the patient to metallic ions within the implanted devices, most notably cobalt. Additionally, concerns exist regarding hypersensitivity, increased incidence of instability, and pathologic changes ranging from dementia to chromosomal abnormalities. Thus, it is imperative to develop a detection method to help patients and physicians quickly diagnose the occurrence of lubrication degradation and impingement.
Although there has been a large amount of research in alternative methods to estimate or measure the thickness of lubrication and to identify lubrication regimes, most systems have astonishingly high requirements for the testing signals and are limited for in vitro tests only. The systems and methods discussed herein allow in situ or in vivo, real-time monitoring of both the lubrication and the structural health of MOM artificial joints. The systems and methods disclosed herein provides a real time, more feasible, and lower cost alternative that helps better characterize and understand the features of degradation of lubrication and other negative scenarios, thereby allowing physicians to quickly diagnose the structural health of joints or implants, thus prolonging the active time of the implants and reducing the chance of needing a revision surgery.